The present invention is a new and improved slab element and ground surface cover arrangements of such elements. The invention provides many of the advantages of my previous invention entitled INTERLOCKING SLAB ELEMENT FOR COVERING THE GROUND AND THE LIKE disclosed in my U.S. Pat. No. 4,544,305, and, in addition providing other desirable and unique advantages and characteristics.
Slab elements of differing shapes have been employed in the construction of traffic-carrying surfaces such as roadways, footways, embankments and pool decks. Typically, the slab elements are made of concrete, formed in desired shape in molds, and cured under high pressure where the slab material is compacted and hardened into the desired shape in the mold, and removed from the mold and exposed to ambient air to complete the curing cycle. The method by which such slab elements can be made are well known in the art and form no part of my invention. Hence, methods for making slab elements will not be addressed further except to note that the shape of the molds used to form prior art slab elements must be modified so as to conform to the shape of my slab elements.
To construct a surface employing slab elements, an under-surface is prepared in known fashion to provide a smooth flat surface upon which to place the slab elements. The slab elements are placed one at a time such that their vertical or peripheral walls or edge faces come into close contact. The gaps between edge faces may be filled either with mortar, concrete, or other such solidifying spacer element, or, preferably, with sand which is simply poured into the gaps in a known manner. My invention is ideally suited to the latter, less costly method. The traffic load encountered by surfaces constructed in the above manner can vary from as light as pedestrian traffic to as heavy as several ton trucks and forklifts.
Slab elements employed for traffic surfaces have come in a wide variety of shapes from square and rectangular to multi-sided and irregular shaped surfaces, but a slab element's shape is known to affect the ground cover's load carrying capacity and durability. When viewed from the top, such slab elements generally fall into one of three basic categories.
The first category is a slab element which has a known and simple geometric shape, such as a rectangle, a square, a hexagon, or an octagon. From an aesthetic point of view, this category of elements is highly desirable and has historically been in great demand. In other respects, this category has heretofore been less desirable than other categories hereinafter discussed because such shapes preclude an interlock joint between adjacent slab elements. Additionally, proper utilization can require greater material and care than other slab elements and are often not satisfactory in use. For example, if such slab elements were placed in the manner expected of my invention, i.e., with sand between them, the surface would not be stable because there is no interlock. Furthermore, because there is no interlock, long, straight channels are more easily formed between the elements thus permitting rain, for example, to wash away the sand further reducing the load carrying stability of the ground cover formed with those elements. Hence, such slab elements would typically require mortar or concrete between elements. Mortar or concrete are typically more expensive than sand and are more difficult to work with.
A second category of slab element is one wherein, from a top plan view, the slab element looks substantially rectangular but the edges are deformed in such a manner as to interlock when laid next to an adjacent, identical stone. Examples of second category slab elements are shown in U.S. Pat. No. 2,919,634 and U.S. Pat. No. 3,494,266. Also included in this category are certain multi-faced irregularly shaped slab elements such as those disclosed in U.S. Pat. No. Des. 82,970. The slab elements disclosed in the aforementioned patents overcome some of the drawbacks of slab elements discussed in the preceding paragraph because they may be interlocked. However, they are less attractive from an aesthetic standpoint. Moreover, the slab elements in this category generally may not be intermixed with other differently shaped second category slab elements as would be possible with first category slab elements to permit a wide variety of patterns to be created.
A third category of slab element, and the one with which my invention is concerned, overcomes the drawbacks of both first and second category slab elements. A third category slab element is comprised of two or more sections having the shape of first category slab elements which are combined into one integral slab element. An example of such a slab element is disclosed in U.S. Pat. No. 4,128,357. The slab element of that patent has a main section which is of a known octagonal shape, and a tail section which is of a known square shape, with the main and tail sections being formed as one slab element. The primary advantage of such an integral slab element is that it can interlock for durability and stability. A disadvantage, however, is that it is susceptible of only a few different interlocking patterns.
In German Patent No. 3,409,114 to Koelling, a variety of patterns are provided with the use of several individual stones of differing shapes, including squares and hexagons. Not only does such a combination of stones require plural stones of different shapes, which is undesirable, but such combination produces a surface which presents problems when subjected to heavy loads, particularly the loads of conventional large trucks, as for example, those having standard dual H-20 wheels.
In my U.S. Pat. No. 4,544,305, I have disclosed a slab element for use in providing a ground cover particularly suited for use filling the joints with sand. In my prior patent, I have taught that the combined shapes of a square and hexagon could be used to form such a slab element when the hexagon has two pair of minor faces equal to those of the square, each pair joined by a right angle with the pair being joined together by two major faces each twice the length of a minor face, the square being joined at a minor face.
In integrating a paving surface pattern into an architectural or landscaping plan, certain designs call for surfaces with the more classical appearance of patterns which are built upon the more regular basic shapes of squares and hexagons. Such patterns are illustrated in British patents of Crannis et al No. 9640 and Dodgson No. 610, German Patent No. 27-51-536. As I have pointed out in my previous U.S. Pat. No. 4,544,305, slab elements combining these shapes for use in a variety of interlocking patterns cannot be easily selected. Where an objective is, however, to provide an interlocking paving element of brittle ceramic material such as concrete, certain other practical problems are presented.
In the art of roofing, for example, where flexible materials are employed, plural square or hexagon shapes can be joined in an integrated covering element with less concern for the structural problems by joining brittle materials, for example, as shown in Abraham U.S. Pat. No. D75,761. In arts requiring ceramic materials, particularly for the formation of thinner tile-like rather than thick block-like elements, the avoidance of thin elongated elements and elements with acute external or internal angles adds to the strength of the element, reduces the incidence of element breakage in manufacture, storage, handling, assembly and use, and enhances the ease of manufacture.
The usual applications for paving stones are aesthetic. The working loads on such pavements are normally pedestrian or light wheel traffic, e.g., automobiles, and for this level the shapes, sizes, colors and thicknesses (usually 60 mm) can be as varied as the customer wishes and can afford. Most such applications are hand-laid, hence the stones are within the 4-6 kg weight and dimensional size that can be comfortably handled in manual placement. The stones specified in my U.S. Pat. No. 4,544,305 and the above-mentioned German Koelling patent are primarily designed for forming a wide variety of visually pleasing geometric patterns.
The paving stone of the present invention is an interlocking stone, which, when subjected to heavy truck wheel loading, is capable of retaining a continuous, smooth plane surface and withstands fracture forces. The stones of my U.S. Pat. No. 4,544,305 and of the German Koelling patent, even though superficially resembling, or producing patterns resembling, those of the present invention, are not satisfactorily capable of heavy truck wheel service. Further, these stones cannot be made capable of satisfactorily withstanding such loads by mere enlarging or reducing the size of the stones, due to unobvious shortcomings in their geometries.
The stone of my U.S. Pat. No. 4,544,305 can create a very large number of varied patterns using only a single style of stone. Its elongated shape, however, limits its inherent load bearing acceptability regardless of the size at which it is made. The Koelling stone set requires several different shapes to create similar or equal patterns. Here too, regardless of the size of these stones, the mere differences in the sizes inhibits the load bearing adaptability of these stones.